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Doctors struggle to contain drug-resistant typhoid 'superbug'

A genetic study of typhoid bacteria has identified an antibiotic-resistant “superbug” strain proliferating at an alarming rate.

Driven by a single family of bacteria, “H58,” a new antibiotic-resistant strain of typhoid fever has spread across the globe. A large internaional study, involving 74 scientists from almost two dozen countries, has identified the new “superbug” strain using one of the most comprehensive sets of genetic data on an infectious pathogen, and worries that the disease could pose an “ever-increasing public health threat.”

Typhoid typically is spread through contaminated food and water, and causes symptoms of nausea, fever, abdominal pain, and pink marks on the chest. The disease is fatal to nearly 20 percent of patients, and can lead to serious complications in the head and gut if left untreated.

Vaccines are available to increase resistance to typhoid infection, but are often too expensive for poor and developing countries to use on a wide scale. Regular strains of the infection can be treated with antibiotics.

Medical professionals are alarmed at the rate at which H58 has proliferated, and have found it to be resistant to multiple types of antibiotics. The superbug strain of typhoid is now the dominant form of the disease, and doctors aren’t quite sure how to respond.

Vanessa Wong of Britain’s Wellcome Trust Sanger Institute, a member of the international team that conducted the study, stated that typhoid affects over 30 million people eaach year. She stressed the importance of robust and detailed global surveillance efforts in trying to contain the ongoing eidemic.

The study sequenced the genomes of 1,832 samples of Salmonella Typhi bacteria, collected from 63 countries between 1992 and 2013. 47 percent of the samples originated from the H58 strain of the bacteria.

According to the study, H58 emerged from South Asia about 25 to 30 years ago. From there, it spread to Southeast Asia, Western Asia, East and South Africa, and Fiji. Recent reports of H58 transmission in certain countries in Africa suggest that the disease is spreading at an alarming rate, what some might even consider an epidemic.

According to Kathryn Holt of the University of Melbourne, the drug-resistant genes found in the H58 strain of typhoid are have become a more stable part of the bacteria’s genome since the 1970s. She thinks the resistance to antibiotic treatments is here to stay.

Resistance to common antibiotic treatments such as ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and streptomycin is increasing at an alarming rate. Multidrug-resistant typhoid has become much more prevalent over the last twenty years, particularly in the Indian subcontinent and Southeast Asia. Doctors are scrambling to find an alternative to the widely-used ciprofloxacin, as it is continually becoming less effective at treating the infection.

Typhoid fever, an infection caused by the Salmonella Typhi bacteria growing in the intestines and the blood, begins with a high fever that rises over the course of a few days. Later symptoms include weakness, abdominal pain, constipation, and headaches. In certain cases, a skin rash develops around the neck and chest with rose-colored spots. Some people don’t suffer from symptoms, but may still be carrying the bacteria.

In rare cases, surgery may be necessary to treat typhoid fever. The bacteria can lead to intestinal perforation, and surgeons may need to close the holes left behind by the bacteria. If further antibiotic treatment fails to eliminate the infection in the gut a cholecystectomy is performed, though there is no guarantee that this will kill off the infection for good.

Without treatment, typhoid symptoms can last for months. It is spread by eating food or drinking water that have been contaminated by the feces of another person infected with the disease. The risk of contracting typhoid is significantly increased by poor sanitation and poor hygiene. Cases are largely concentrated in the developing world.

There are vaccines that can prevent up to 70% of typhoid infections for up to seven years, but access in developing countries is dangerously limited. 27 million cases were reported in 2010, with the highest concentration in India. The United States reports roughly 400 cases each year, though medical researchers estimate that up to 6,000 people are actually infected each year.

Without treatment, up to 25 percent of infected people will die from the fever, whereas the survival rate with treatment is about one to four percent.

The United States Centers for Disease Control and Prevention (CDC) has reported that the widespread chlorination of drinking water supplies has resulted in dramatic drops in typhoid transmission in the U.S. The presence of fecal bacteria in water and on food that has come in contact with with that water is the primary cause of typhoid infection, which only affects humans.

Typhoid cases were reported as far back as 430 B.C., in a plague that killed nearly one-third of the population of Athens. A 2006 study of DNA extracted from dental pulp found in a burial pit dated to the time of the outbreak stated that typhoid fever was a probable suspect in the Plague of Athens.

The study was published in Nature Genetics this Monday.

 

 

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